There are a wide variety of applications that require the identification and registration of a surface or shape with a previously created image. Certain manufacturing systems use the placement of tracking devices in predetermined locations to track the position of a work piece relative to an industrial process. Another use of this type of tracking system is in computer assisted or image guided surgical navigation systems.
The use of surgical navigation systems for complex surgical procedures has become relatively widespread. These surgical navigation systems use specially developed tools that include tracking devices so that the surgeon can see the position of the surgical tool overlaid on a monitor showing a preoperative or intraoperative image. The preoperative images are typically prepared using well-known preoperative scanning techniques, such as MRI or CT scans. The intraoperative images can be prepared using a fluoroscope, a low level x-ray, and similar devices. Tracking devices typically include multiple optical emitters such as LED's that can be detected by the surgical navigation system. The surgical navigation system can determine the position and/or orientation of the surgical tool from the position of the emitters.
In addition to tracking the surgical tool, the surgical navigation systems also must track or register the preoperative or intraoperative images to the patient in the operating arena so that the coordinate systems for the image files match the coordinate systems for the surgical navigation system. Typical registration procedures include placing fiducials or other markers at various locations on the anatomy of the patient. The preoperative or intraoperative scan is then performed with these markers in place and the markers then are either left in place until the surgery occurs or reapplied in the same position immediately prior to surgery. During the setup procedure before the surgical procedure, the scanned images in the computer are then registered to the patient by matching the location of these markers in the scanned images with the position of the actual markers on the patient in the surgical arena. Because the matching of the exact locations of these markers is critical to successful registration, the prior methods of attaching these markers usually involve an invasive procedure, such as attaching the markers themselves or a clamping device that carries the markers to bony areas of the patient. Alternatively, surgical personnel may use a permanent or semi-permanent marker to mark the patient at the locations where the markers or the clamping device are to be reapplied.
It is well recognized that the prior techniques are uncomfortable for the patient and often leave permanent marks or scarring. As a result, there have been numerous attempts to create less invasive markers for use in the registration of scanned images to the coordinate system of the surgical navigation system at the time of surgery.
In U.S. Pat. Nos. 6,122,541 and 6,248,900, a headband for frameless stereotatic registration is disclosed. This headband has markers, which can be visualized in the preoperative image scan and also includes LED's so that the headband can act both as a registration aid and as a tracking device for the patient during surgery. The system is registered during surgery by the standard registration practice of touching the tip of a tracking probe to each reference marker prior to beginning the surgical procedure.
U.S. Pat. No. 5,676,673 discloses a headset to be mounted on the patient. The headset is used to mount a reference unit such as magnetic field generator to track a surgical instrument inside the patient relative to the preoperative image. Registration of the image to the patient is accomplished using conventional fiducial type markers attached to the patient's skin.